unilateral LMN lesion of CN VII or its nucleus

What is a common cause of LMN lesions to CN VII?

Bell's Palsy

What type of lesion causes weakness of contralateral shoulder elevation and weakness of ipsilateral SCM muscle (turning head away from lesion)?

unilateral UMN lesion of CN XI

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Why do UMN lesions to CN XI affect the trapezius and SCM of different sides?

UMNs for the SCM descend ipsilaterally to the spinal accessory nucleus while the UMNs for the trapezius muscle cross the midline in the pyramidal decussation to synapse in the contralateral spinal accessory nucleus

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What type of lesion causes hoarseness, dysphagia, inability to elevate palate on ipsilateral side as well as a reduced gag reflex?

unilateral LMN lesion to CN X or its nucleus

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Why do UMN lesions to CN X not cause the same symptoms as LMN lesions?

Substantial bilateral upper motor neuron innervation of CN X nuclei

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What would you expect to see with a unilateral LMN lesion to CN XI?

Weakness and atrophy of both muscles ipsilateral to lesion—weakness elevating the shoulder and turning head away from lesion side.

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What would you expect to see with a unilateral LMN lesion to CN XII?

Tongue protrusion towards the side of the lesion, unilateral atrophy and fasciculations

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How do you test for CN V?

Test by having patient bite down on tongue depressor and test jaw strength; palpate masseter and temporalis bilaterally.

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What does the "jaw jerk reflex" test for?

assess function of motor nucleus of V and mesencephalic nucleus as well as the third branch of the trigeminal nerve (mandibular) carrying the fibers

What is the "jaw jerk reflex"?

How do you test for CN VII?

Test by having patient wrinkle forehead, close eyes tightly, and show you their teeth. Look for symmetric furrowing of forehead, ability to symmetrically close eyes, and symmetric retraction of the corners of the mouth.

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How do you test for CN IX and X?

Integrity tested via the gag reflex ( IX carries afferent/sensory arm of the reflex but shares efferent part of the reflex with CN X). Stimulate reflex by gently touching posterior pharynx on left and right side separately and watching for the motor, or gag response and elevation of soft palate

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After synapsing in the nucleus solitarius, where do the secondary neurons from the Gag Reflex go?

secondary fibers project to the nucleus ambiguous where they synapse so that visceral efferents (traveling with the vagus nerve) can reach the pharynx and mediate the gag reflex

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How do you test for CN XI?

Test by getting patient to raise shoulder and look in opposite directions bilaterally.

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How do you test for CN XII?

Test by getting patient to stick tongue out (make sure it is sticking straight out at midline)